One type of a conventional data bus coupler design corresponds to military standard MIL-STD-1553B. Such a design is shown and referred to in FIG. 3 and is comprised of an electrically shielded housing 11, through which a bus line piece 13 is passed. The bus line piece 13 has a first bus line wire 15 and a second bus line wire 17. A data bus connector 19 or 21 is connected to each end of the bus line piece 13. The data bus connector 19 or 21 enables the bus line piece 13 to be releasably connected to a bus line (not shown). A transformer 23 having a primary winding 25 and a secondary winding 27 is also situated in housing 11. The two terminals of primary winding 25 are connected via two coupling resistance elements 29 and 31 to the first bus line wire 15, or to the second bus line wire 17. The two terminals of the secondary winding 27 are connected to a branch line connector 33, which serves to connect a branch line (not shown) to the secondary winding 27 of transformer 23.
A coupler housing 11 may comprise several data line couplers each with a coupling resistance pair and a transformer. This is shown in FIG. 3 by a second data bus coupler indicated by dashed lines.
The coupling resistance elements 29 and 31 are provided to protect the two bus lines wires 15 and 17 from a direct short circuit. This series circuit from the two coupling resistance elements 29, 31, and the primary winding 25 connected between the two bus line wires 15 and 17, represents a load for the bus line 13. Such a load causes a disturbance in the characteristic impedance of the bus line 13, which in turn increases with the length of the branch line to be connected via the coupler to the two bus line wires 15 and 17. As may be appreciated by one skilled in the art, when a number of such data bus couplers are connected to the bus line 13, the resulting total load and resulting total characteristic impedance mismatch may cause a significant adverse effect on the electrical behavior of a bus line system.
In designing a bus line system for an aircraft, for example, it is desirable to incorporate the largest possible number of reserve couplers in the data bus system so that additional remote devices can be connected to the data bus system at a future time. However, to minimize the total load and total characteristic impedance mismatch for such a bus line system, reserve couplers are not provided in a bus line system unless absolutely required.
The foregoing illustrates limitations known to exist in present line couplers. Thus, it is apparent that it would be advantageous to provide an improved line coupler directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.